In radial flow processes, the reactor typically comprises scallop-shaped conduits or screens, hereinafter referred to as “scallops”, installed adjacent to and vertically along the inside wall of a cylindrical reactor. The scallops are typically 8 to 14 inches wide and designed with a scallop-like cross-sectional shape (e.g., semi-circular or arced) to fit against the inside wall of the reactor. After installation and catalyst loading, the scallops distribute a hydrocarbon feed along the inside wall. The feed then flows radially to the center of the reactor across a fixed catalyst bed. In the center of the reactor is the process outlet conduit, which is a vertical perforated pipe, also referred to as a center pipe.
The base of each scallop rests in a fixed bottom wall ring just above the bottom head of the reactor and extend almost the full length of the inside vertical wall of the reactor. Just below and inside the top head of the reactor are cover plates that traditionally are bolted to the center pipe and extend in a pie shaped fashion from the center pipe to the top of the scallops. These cover plates help seal the top side of the catalyst bed and distribute incoming flow of hydrocarbon feed gas into the scallops. As a result, the reactor scallops are firmly confined between the top cover plates and the bottom wall ring.
As the reactor internals (e.g., the scallops and the center pipe) are heated, they may expand longitudinally from thermal expansion. Often a radial temperature gradient exists across the catalyst bed. When an endothermic reaction occurs in the catalyst bed the temperature near the reactor walls may be higher than at the center pipe. As a result, the scallops may be subjected to a higher temperature and experience a greater longitudinal expansion than the center pipe that is at a lower temperature. Because of the greater expansion of the scallops relative to the center pipe, the scallops may be subjected to a compressive force between the bottom wall ring and the top cover plates, which may cause deformation of the scallops. This deformation results in a “bowing” of the scallops away from the wall of the reactor which crushes catalyst, disrupts the feed flow patterns, and allows catalyst to migrate between the scallops and the reactor wall. All of these are undesirable. Furthermore, the bowed scallops require extensive repair or replacement. Therefore, there is a need in the art for alternative top cover plate designs for radial flow reactors to allow for thermal expansion of the reactor internals.